1. Field of the Invention
The present invention is directed in general to a field of information processing. In one aspect, the present invention relates to a system and method for transmitting channel feedback information from one or more receivers.
2. Description of the Related Art
Wireless communication systems transmit and receive signals within a designated electromagnetic frequency spectrum, but capacity of the electromagnetic frequency spectrum is limited. An example of such a wireless communication system is a Multiple Input Multiple Output (MIMO) system, such as the 3GPP LTE (Long Term Evolution) system depicted in FIG. 1, which schematically illustrates the architecture of an LTE wireless communication system 1. As depicted, the broadcast server 28 communicates through an EPC 26 (Evolved Packet Core) which is connected to one or more access gateways (AGW) 22, 24 that control transceiver devices 2, 4, 6, 8 which communicate with the end user devices 10-15. In the LTE architecture, the transceiver devices 2, 4, 6, 8 may be implemented with base transceiver stations (referred to as enhanced Node-B or eNB devices) which in turn are coupled to Radio Network Controllers or access gateway (AGW) devices 22, 24 which make up the UMTS radio access network (collectively referred to as the UMTS Terrestrial Radio Access Network (UTRAN)). Each transceiver device 2, 4, 6, 8 includes transmit and receive circuitry that is used to communicate directly with any mobile end user(s) 10-15 located in each transceiver device's respective cell region. Thus, transceiver device 2 includes a cell region 3 having one or more sectors in which one or more mobile end users 13, 14 are located. Similarly, transceiver device 4 includes a cell region 5 having one or more sectors in which one or more mobile end users 15 are located, transceiver device 6 includes a cell region 7 having one or more sectors in which one or more mobile end users 10, 11 are located, and transceiver device 8 includes a cell region 9 having one or more sectors in which one or more mobile end users 12 are located. With the LTE architecture, the eNBs 2, 4, 6, 8 are connected by an S1 interface to the EPC 26, where the S1 interface supports a many-to-many relation between AGWs 22, 24 and the eNBs 2, 4, 6, 8.
As will be appreciated, each transceiver device (e.g., eNB 2) in the wireless communication system 1 includes a transmit antenna array and communicates with receiver device (e.g., user equipment 15) having a receive antenna array, where each antenna array includes one or more antennas. The wireless communication system 1 may be any type of wireless communication system, including but not limited to a MIMO system, SDMA system, CDMA system, SC-FDMA system, OFDMA system, OFDM system, etc. Of course, the receiver/subscriber stations (e.g., user equipment 15) can also transmit signals which are received by the transmitter/base station (e.g., eNB 2). The signals communicated between the receiver/subscriber stations and transmitter/base station can include voice, data, electronic mail, video, and other data, voice, and video signals.
Various transmission strategies require the transmitter to have some level of knowledge concerning the channel response between the transmitter and each receiver, and are often referred to as “closed-loop” systems. An example application of closed-loop systems which exploit channel-side information at the transmitter (“CSIT”) are precoding systems, such as space division multiple access (SDMA), which use closed-loop systems to improve spectrum usage efficiency by applying preceding at the transmitter to take into account the transmission channel characteristics, thereby improving data rates and link reliability. SDMA based methods have been adopted in several current emerging standards such as IEEE 802.16 and the 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) platform. With such preceding systems, CSIT can be used with a variety of communication techniques to operate on the transmit signal before transmitting from the transmit antenna array. For example, preceding techniques can provide a multi-mode beamformer function to optimally match the input signal on one side to the channel on the other side. In situations where channel conditions can be provided to the transmitter, closed loop methods, such as MIMO preceding, can be used. Precoding techniques may be used to decouple the transmit signal into orthogonal spatial stream/beams, and additionally may be used to send more power along the beams where the channel is strong, but less or no power along the weak, thus enhancing system performance by improving data rates and link reliability. In addition to multi-stream transmission and power allocation techniques, adaptive modulation and coding (AMC) techniques can use CSIT to operate on the transmit signal before transmission on the transmit array.
With conventional closed-loop MIMO systems, full broadband channel knowledge at the transmitter may be obtained by using uplink sounding techniques (e.g., with Time Division Duplexing (TDD) systems). Alternatively, channel feedback techniques can be used with MIMO systems (e.g., with TDD or Frequency Division Duplexing (FDD) systems) to feedback channel information to the transmitter. One way of implementing channel information feedback is to use codebook-based techniques to reduce the amount of feedback as compared to full channel feedback. However, even when codebook-based techniques are used to quantize the channel feedback information, feedback from multiple receivers can cause an uplink bottleneck. Specifically, allowing all users to feedback causes the total feedback rate to increase linearly with the number of users, placing a burden on the uplink control channel shared by all users (e.g., as proposed by 3GPP LTE). Prior solutions to the uplink bottleneck problem have attempted to schedule the feedback of channel quality indicator (CQI) reports from different user equipment (UE) receivers by periodically feeding back CQI reports from each UE at regular or predetermined intervals so that the base station can assemble and use the CQI reports to schedule UEs for transmission. Typically, the base station (e.g., eNB 8) controls the scheduling of CQI feedback from its UEs (e.g., UE 12) by transmitting configuration messages to each UE that include a “start” message (e.g., 16) and a subsequent “stop” message (e.g., 17) to start and stop the periodic CQI feedback, and also a “change rate” message (not shown) which changes the period of the CQI reporting if required. Between the start and stop messages (e.g., 16, 17), the UE generates periodic CQI reports (e.g., 21) that are fed back to the base station. Over the course of time 23, the process is repeated by sending additional start and stop messages (e.g., 18, 19) to enable each UE to send back periodic CQI reports (e.g., 23). However, there is a significant amount of feedback control channel overhead (and associated bandwidth) required to configure periodic CQI reporting by transmitting the “start” and “stop” messages to each UE, particularly when there are many UEs in a cell. In addition, there is a significant amount of feedback control channel overhead (and associated bandwidth) required for feeding back periodic CQI reports from all UEs in a cell which can impair uplink performance by overwhelming and/or delaying CQI feedback reporting.
Accordingly, an efficient feedback methodology is needed to provide the channel information to the transmitter while reducing the amount of required overhead. Further limitations and disadvantages of conventional processes and technologies will become apparent to one of skill in the art after reviewing the remainder of the present application with reference to the drawings and detailed description which follow.